As shown in FIG. 1, a refrigerator, which is typically used, comprises an evaporator 10, an impeller part 12 and a condenser 14 and has such a structure that the evaporator 10, the impeller part 12 and the condenser 14 are organically connected to each other to circulate the refrigerant. To be more specific, the refrigerant is transferred from the evaporator 10 to the condenser 14 through a discharge pipe 16 via the impeller part 12 compressing the refrigerant. At this time, a traveling sound wave 22, which is generated while the impeller part 12 compresses and discharges the refrigerant to the discharge pipe 16, is spread along the discharge pipe 16. However, since the discharge pipe 16 has a hollow structure having a constant inner diameter, it is impossible to reduce the traveling sound wave 22 that travels along the discharge pipe 16, which causes the serious noise pollution.
In order to solve the above problem, it has been used a method wherein a separate silencer or resonator is installed in the discharge pipe 16 to cause an acoustic resonance, thereby reducing the noise. According to the conventional method, the silencer or resonator is inserted into the discharge pipe 16 and is then fixed to the discharge pipe 16 using a welding and the like. Therefore, it is not easy to install the noise reduction apparatus. In addition, the acoustic absorption/sound isolation means may be provided to a periphery of the discharge pipe 16 or refrigerator. However, such method increases the related costs.